1. Field of the Invention
This invention relates to wave transmission and, more particularly, to circuit arrangements for automatically balancing hybrid networks.
2. Description of the Prior Art
In many signal transmission applications where bidirectional communication is carried over cable, signals traversing the two directions need to be periodically separated so that they may be amplified. Signal separation is generally accomplished in a four port biconjugate network, known as a hybrid (and hereinafter so called), by connecting the bidirectional cable to one preselected port of the hybrid and by connecting a proper balancing network to another preselected port of the hybrid. The separated signals appear at the remaining two ports of the hybrid, whereto the unidirectional lines are connected.
In order to achieve hybrid balance, and, thus, proper signal separation, it is known that the impedance of the balancing network must closely match the impedance of the bidirectional cable. An impedance mismatch between the bidirectional cable and the balancing network can result in signal reflections which, in turn, can result in unacceptable return-loss performance, in instability of amplifiers in the telephone circuits, or in echoes which are subjectively objectionable to the telephone user.
Because present day telephone transmission facilities exhibit a wide range of impedances, it has often been necessary to either construct precision balancing networks which would manually be adjusted to match the line impedance of a number of installations, or to manufacture a large number of different balancing networks. In both cases, prior art balancing networks have often been complex and rather large in size.